Braun tube



NOV. 30, 1937. K, SCHLESWGER 2,100,701

BRAUN TUBE Filed Oct. 18, 193;

Jill e0 for:

Patented Nov. 30, 1937 UNITED STATES BRAUN TUBE Kurt Schlesinger,

Application October 18,

In Germany 8 Claims.

It is known that the effect in connection with Braun tubes known as the lateral pull is produced by errors in the centring of the system, and more particularly by incorrect arrangement of the cathode. It has also already been proposed for overcoming this error to arrange the cathode exactly centrally in relation to the anode aperture. These known arrangements, however, have not proved to be sufiicient to overcome the lateral pull defect.

The term lateral pull defect means a nondesired efiect produced by the control electrode, which consists in that each change in the control voltage causes not only the desired change in the intensity. of the cathode ray but simultaneously a non-desired change in the direction of the cathode ray which results in a non-desired displacement of thespot on the fluorescent screen.

The applicant has found that it is not the arrangement of the entire cathode with respect to the anode but the form and size-of the emissive coating and its position with respect to the other electrodes and especially with respect to the control electrodewhich are responsible for the occurrence of this error.

According to the invention, the emissive coating. is embodied and arranged symmetrically on the cathode in relation to the axis of the tube, in such fashion that the normal on all lines connecting. eachtwo corresponding points of the curve bounding the emissive layer coincides with the axis of the tube. At. the same time the size of the'emissive coating is such that the emission of all emissive points is covered by the electron optic.

The term -electronoptic means one electronoptical system or a plurality of electron-optical systems which are provided in the .tube for the purpose of producing ,on the picture receiving screen an ,imagepoint representing a sharppicture eitherof the cathode itself or of a suitable aperture which is arranged between the cathode and the electron-optical system and acts asthe proper cathode of the tube.

The electron-optical system of television tubes-which may consist, for example, of Wehnelt cylinder, preliminary or screening anode, second cylinder and after-acceleration anode, the preliminary anode being positive in relation to the Wehnelt cylinder, the second cylinder weakly negative in relation to the screening anode, and :he after-acceleration anode possesses the highest positive potential occurring-possesses in practice a relatively small aperture of, for example, approximately 10", i. e., it is not able to Berlin, Germany 1933, Serial No. 694,134 ctober 21, 1932 concentrate rays which form with the system axis an angle of more than 10.

According, therefore, to the invention, the emissive coating is embodied in such fashion that none of the output normals possesses in relation to the axis of the tube an inclination which is greater than the aperture of the electron-optical system employed.

It has been found to be particularly convenient toselect the curvature of the emissive coating with consideration to the curvature possessed by the level 0 shortly before reaching the surface of the cathode, viz., to select the curvature of the emissive surface to be equal to or greater than the curvature of the said level in the stated position.

The term level 0 means the curved plane connecting all of the points in the vicinity of the cathode, the potential of which is zero. The position and the curvature of this plane is defined by the potentials of the cathode and of the control electrode and by the arrangement of these electrodes with respect to one another and to the anode. The position and curvature of the lever 0 changes in correspondence with the changes of the control potential applied to the control electrode in such a way, that it moves the more in the direction to the cathode surface the more positive the control electrode becomes, until at last it coincides with the emissive surface.

By adopting the measure according to the invention when producing cathodes it is possible to produce tubes, which are absolutely free of lateral pull, and in which lateral pull does not take place even when the cathode has become partially aged.

A form of embodiment of the cathode according to the invention is illustrated by way of example in the drawing, in which Fig. 1 is a section through the complete cathode arrangement.

Fig. 2 is a plan view of the same arrangement, whilst in Fig. 3 there is shown a particular form of embodiment of the cathode member, and in Fig. 4 a plan view of this member.

Fig. 5 is a diagrammatic sectional elevation of a cathode ray tube comprising a cathode arrangement according to the invention.

In the drawing l is the Wehnelt cylinder, which is centered in such fashion by means of the holder ll}- that its axis coincides with the axis of the tube. In this Wehnelt cylinder there is fitted a pot 2, which serves for exact centring of the cathode system in the Wehnelt cylinder, and: 55

and 5 composed of ceramic material. The tube 5 carries at its upper end pro ecting out of the for the heating current and carries the metallic, preferably nickelcathode member 3. The sleevelike cathode member 3 is made in the form of a hollow reflector at its upper, preferably widened end, the centre of curvature being disposed on The emissive substance, for example an alkaline earth oxide or a mixture of alkaline earth metal oxides and alkaline earth metals, may be applied to the surface of the hollow reflector by painting or the like. It has been found, however, that in this manner exact confinement of the emissive surface is not to be obtained. According, therefore, to the invention, the surface in the hollow reflector intended for reception of the emissive substance is engraving, milling or the like, and the recess formed in this fashion is filled out with the emissive substance. After the filling in and drying of the emissive substance the surface, if necessary, may again be polished, so that the emissive substance itself forms part of the hollow reflector, and is contained solely in the recesses provided for the same, which recesses possess an exactly pre-determined form. In this manner it is possible to give the emissive surface an exactly defined piedetermined shape.

It is particularly convenient to produce in the surface of the hollow-reflector, for example by milling, an elongated slot, which may possess, for example, the dimensions of .5-1 mm. in Width and 2-3 mm. in length, and the greatest extension of which is disposed vertically to the line direction. When employing cathodes of this nature it is possible to produce points of corresponding rod-like form, which for the first time permitof the production of a line screen, the single lines of which are disposed in close proximity to one another without intermediate spacings.

A cathode of this type is illustrated in Figs. 3 and 4. The emissive substance is provided in the preliminarily engraved or milled slot II, in such fashion that the emissive surface possesses the requisite curvature according to the invention, and that no additional emissive centres of any kind are present outside of this emissive surface.

In the form of embodiment according to Fig. 1 the emissive substanceis represented as grain point I I.

The embodiment of the cathode with the massive metallic cathode body 3 according to the invention prevents in reliable fashion a variation in the form of the emissive surface upon the assembly. Owing to the fact that thicker emissive coatings-which represent a greater reserveare employed, a partial burning out of the emissive surface and accordingly a variation in the effective surface in operation will be safely avoided for a period of several thousand hours.

In Fig. 5 the following additional references are used: l3 for the second cylinder, l4 for the after-acceleration anode, and I5 for the envelope 'of the cathode ray tube.

No specific shapes or arrangement of the individual elements are to be read on this merely diagrammatic showing.

Naturally it is possible to secure the cathode member 3 also in other fashion. The essential this cathode body be of such a. stable kind that it cannot be distorted either upon the assembly or in operation or otherwise vary its form.

The concentration effect which is capable of being obtained with the assistance of the cathode arrangement according to the invention is so considerable that it is possible, particularly when employing the Braun tube for osciliographic purposes, to dispense with Wehnelt cylinder, or to link up the Wehnelt cylinder with zero potential and employ the same solely as light screen.

I claim:

1. In a Braun tube in combination with a picture receiving screen and an electro-static electron opticai system having an aperture angle of at least 10 degrees: a structural unit producing a bundle of cathode rays, the angle of inclination of which with respect to the tube axis does not exceed 10 degrees for the purpose of causing the electron optical system to collect all of the electrons produced by said unit for forming one sharp image on the image screen, said structural unit comprising an indirectly heated cathode body, a highly emissive surface covering a partial area of the surface of the cathode body facing the electron optical system, said structural unit further comprising a control electrode, said highly emissive surface being disposed symmetrically with respect to said control electrode.

highly emissive layer disposed in a recess occupystructural unit further comprising a control elec trode, said highly emissive surface being disposed symmetrically trode.

3. In a Braun tube in combination with a. picture receiving screen and an electro-static electron optical system having an aperture angle of at least 10 degrees: a structural unit producing a bundle of cathode rays, the angle of inclination of which with respect to the tube axis does not exceed 10 degrees for the purpose of causing the electron optical system to collect all of the electrons produced by said unit for forming one sharp image on the image screen, said structural unit comprising an indirectly heated cathode body, the surface of said cathode body facing the electron optical system being curved, a highly emissive surface covering a partial area of the surface of the cathode body facing the electron optical system, said structural unit further comprising a control electrode, said highly emissive surface being disposed symmetrically with respect.

to said control electrode.

4. In a Braun tube in combination with a picture receiving screen and an electro-static electron optical system having an aperture angle of at least 10 degrees: a structural unit producing with respect to said control eleca bundle of cathode rays, the angle of inclinatron optical system having an aperture angle of at tion of which with respect to the tube axis does least 10 degrees: a structural unit producing a not exceed 10 degrees for the purpose of causing bundle of cathode rays, the angle of inclination the electron optical system to collect all of the of which with respect to the tube axis does not electrons produced by said unit for forming one exceed 10 degrees for the purpose of causing the sharp image on the image screen, said structural electron optical system to collect all of the elecunit comprising an indirectly heated cathode trons produced. by said unit for forming one body, a highly emissive layer of at least millisharp image onthe image screen, said structural metre thickness disposed in a recess occupying unit comprising an indirectly heated cathode a partial area of the surface of the cathode body body, a highly emissive surface covering a partial facing the electron optical system, said structural area of the surface of the cathode body facing unit further comprising a control electrode, said the electron optical system, said structural unit highly emissive surface being disposed symfurther comprising a control cylinder, a metallic metrically with respect to said control electrode. cathode holder tightly fitting into said control 5. In a Braun tube in combination with a piccylinder, said cathode body being mounted on ture receiving screen and an electro-static elecand insulated from said cathode holder, said tron optical system having an aperture angle of at highly emissive surface being disposed symmetrileast 10 degrees: a structural unit producing a cally with respect to said control electrode. bundle of cathode rays, the angle of inclination of 7. An indirectly heated cathode comprising a which with respect to the tube axis does not exheater element, an equipotential bodymounted ceed 10 degrees for the purpose of causing the near said heater element, part of said equipotenelectron optical system to collect all of the electial body being a mirror surface hollow member, trons produced by said unit for forming one the surface of the hollow member having a recess, sharp image on the image screen, said structural and a highly emissive substance disposed in said unit comprising an indirectly heated body, the recess. surface of said cathode body facing the electron 8. An indirectly heated cathode comprising a optical system being curved, a highly emissive heater element, an equipotential body mounted layer disposed in a recess occupying a partial near said heater element, part of said equipotenarea of the surface of the cathode body facing tial body being a mirror surface hollow member, the electron optical system, said structural unit the surface of the hollow member having a refurther comprising a control electrode, said highly cess, and a highly emissive substance disposed in emissive surface being disposed symmetrically said recess, the surface of the emissive subtance with respect to said control electrode. forming together with the non-emissive parts of 6. In a Braun tube in combination with a picthe hollow member a uniform concave surface. ture receiving screen and an electro-static elec- KURT SCHLESINGER. 

